RTMPDump core dump
Monday, July 15. 2013
Occasionally I like to stea.... erhm.... listen to stuff from Finnish Broadcasting Company's internet-site. Most of the items they have there have some sort of limit, for example 7 days or 30 days, after which the show if off-the-air for good. The technology they're using is streaming FLV, or RTMP, making it relatively easy to steal... ermhm... borrow.
On my Fedora 19 my favorite utility for doing the ste... well... stream-redirection is YLE-DL. It is a Python-wrapper for the classic RTMPDump-utility. The Python-thingie is very much needed, as the parameters required for RTMPDump can be for example:
--playpath=mp3:areena/fi/52/52cf454f9e444f498352f65cfe7ba11d \
--swfUrl=http://areena.yle.fi/static/player/1.2.8/flowplayer/flowplayer.commercial-3.2.7-encrypted.swf \
"--app=ondemand?_fcs_vhost=cp157366.edgefcs.net&auth=eb.bEdRbFdlamabdgckdRcxdvaGbxdvbZbWbscycAdcdKbncbcpbIdSdgdLbidebVbx-br5atj-c0-vga-oxmCrAxmpvkzsqrzxlzp-kblXn9lakal5nTlfn2k6kRnZ&aifp=6&slist=areena/fi/52/52cf454f9e444f498352f65cfe7ba11d" \
--pageUrl=http://areena.yle.fi/radio/1943628 \
--rtmp=rtmpe://cp157366.edgefcs.net/ondemand \
"--tcUrl=rtmpe://217.212.252.204/ondemand?_fcs_vhost=cp157366.edgefcs.net&auth=eb.bEdRbFdlamabdgckdRcxdvaGbxdvbZbWbscycAdcdKbncbcpbIdSdgdLbidebVbx-br5atj-c0-vga-oxmCrAxmpvkzsqrzxlzp-kblXn9lakal5nTlfn2k6kRnZ&aifp=6&slist=areena/fi/52/52cf454f9e444f498352f65cfe7ba11d" \
-o "Parasta ennen! pe klo 20.00-2013-07-12.flv"
This nice script does all that for me. Except it doesn't work. It just says "Segmentation fault (core dumped)". Which is rather bad. 
After very short period of GDBing, I realized that some function-API changed drastically. In this case it is Diffie-Hellman -function in the GnuTLS-library, which RTMPDump can use if chosen to do so. The API-changed for example in gnutls_calc_dh_secret()-function:
Old:
bigint_t
gnutls_calc_dh_secret (bigint_t ret_x, bigint_t g, bigint_t prime)
New:
int
gnutls_calc_dh_secret (bigint_t ret_y, bigint_t * ret_x, bigint_t g, bigint_t prime,
unsigned int q_bits)
Since that function is not in the GnuTLS public API, developers of RTMPDump had to declare that function in their code to make it work. That is because gcrypt and GnuTLS are using multi precision integers to process public-key -stuff. It is much easier to multiply two huge numbers with a suitable library. In this case the libraries should be compliant with each other, but ... Having void-pointers makes it compile, but it doesn't make it run. Without core dumps, that is.
The solution is not to use GnuTLS, which seems to be the default. I chose to use OpenSSL-functions instead. That builds and runs.
Tip:
To get a core dump in Fedora 19 the automatic bug reporting tool ABRT needs to be tweaked. As a default it gets all the cores, not you. See /proc/sys/kernel/core_pattern, which out-of-the-box has value of |/usr/libexec/abrt-hook-ccpp %s %c %p %u %g %t e
So it is a very good idea to edit the value of DumpLocation-directive in /etc/abrt/abrt.conf. I put it like this and created the directory:
MaxCrashReportsSize = 0
DumpLocation = /var/spool/abrt
Then I could get a directory like /var/spool/abrt/ccpp-2013-07-15-17\:30\:42-7463/ containing a coredump-file with the exact point of the crash.
